Chain-tensioner with mechanical locking

ABSTRACT

The present invention relates to a tensioner for endless driving elements, such as chains, belts etc., comprising a tensioning piston provided with locking means, and a locking piston which is implemented such that it is adapted to be engaged with and disengaged from said locking means so as to arrest or release the movement of said tensioning piston, said locking piston comprising an operating section causing said locking piston to move to the arresting position and to the release position, and a locking area used for engagement with said locking means of the tensioning piston and arranged separately from said operating section.

[0001] The present invention relates to a tensioner for endless drivingelements, such as chains, belts etc., comprising a tensioning pistonprovided with locking means, and a locking piston which is implementedsuch that it is adapted to be engaged with and disengaged from saidlocking means so as to arrest or release the movement of said tensioningpiston.

[0002] Such a tensioner is known e.g. from EP 0 657 662 A 2. This chaintensioner comprises a tensioning piston having a plurality of lockinggrooves on the outer circumference thereof, said locking grooves beingengaged by a spring-loaded locking piston. The front face of saidlocking piston is bevelled and can be acted upon by an oil pressure soas to disengage said locking piston. The locking means guarantees that alocking effect is produced when the engine oil hydraulic system isswitched off and that the locking piston can no longer re-tract. Thishas the effect that a certain pretension is maintained, even if theengine is at rest, in spite of possible oil leakage from the pressurechamber. Hence, a predetermined tension, which is independent of theengine oil hydraulic system, will exist when the engine is started. Assoon as sufficient pressure has built up, the locking means will bedisengaged and the tensioning piston will operate in the usual way.

[0003] A similar tensioner is known e.g. from DE 195 48 923 A1. Inaddition, conventional locking devices are provided on chain tensionersand the like, but these locking devices only serve to carry out areadjustment and to limit the retraction path of the tensioning pistonto a pre-determined value. Such structural designs are used for wearcompensation. Locking de-vices connected to the engine oil hydraulicsystem are disadvantageous insofar as they are subjected to thefluctuations of the hydraulic pressure and to a possible pressurebuild-up in the area of the tensioning piston. In the case ofconventional locking devices, the locking piston is forced back by theteeth on the tensioning piston against the force of a spring, and thiswill entail wear.

[0004] It is therefore the object of the present invention to improvethe structural design of a ten-sioner of the type mentioned at thebeginning.

[0005] In accordance with the present invention, this object is achievedby the features that the locking piston comprises an operating sectioncausing said locking piston to move to the arresting position and to therelease position, and a locking area used for engagement with saidlocking means of the tensioning piston and arranged separately from saidoperating section. Due to the fact that the operating point of thelocking piston and the point of en-gagement are separated from oneanother, it is no longer necessary that the locking area is acted uponby operating forces so as to disengage the locking piston. In the caseof hydrau-lically operated tensioners this means e.g. that the lockingarea of the locking piston need no longer be exposed directly to theengine oil hydraulic pressure. Actuation in one direction (arrestingposition) as well as in the other direction (release position) takesplace at some other point. A great variety of operating mechanisms forachieving a piston movement can be employed. This separation of thelocking function and of the operating function also permits the lockingpiston to be controlled in a purposeful manner in dependence upon theoperating parameters. Conventional locking devices of the readjustmenttype as well as locking devices which are readjustable by an engine oilhydraulic system are always pro-vided with operating means actingdirectly on the locking area.

[0006] According to an advantageous embodiment, the operating section ofthe locking piston can be provided with a piston area which is adaptedto have applied thereto an operating pres-sure of a hydraulic fluid, theoperating direction of said piston area being directed towards therelease position of the locking piston. This measure has the effect thatthe locking piston will be displaced to the release position in responseto application of a hydraulic pressure. Such a structural design couldbe used in internal combustion engines and connected to the engine oilhydraulic system.

[0007] In accordance with a preferred embodiment, a spring means can beprovided, which acts on the operating area of the locking piston andwhich is effective in the direction of the ar-resting position of saidlocking piston. This measure has the effect that the locking piston isprimarily forced into the arresting position by the spring force of thespring means. This means that an operating force in the oppositedirection must always be larger so as to cause unlocking.

[0008] According to an advantageous embodiment, the locking area of thelocking piston can be designed such that a hydraulic force balance iscaused. Such a structural design allows the locking area of the lockingpiston to be subjected to a pressure medium, without said pres-suremedium causing any essential force component on the locking area foroperating the locking piston. A person skilled in the art knows that, inorder to achieve this, he must cause forces to act in oppositedirections so that these forces will compensate each other (as far asthe actuation is concerned). Hence, such a tensioner could definitely bearranged in the pressure chamber of the tensioning piston; pressurefluctuations of the pressure in the pressure chamber will not have anyinfluence on the operation of the locking piston, neither into thearresting position nor into the release position. In hitherto useddevices comprising controlled locking devices, such pressurefluctuations have always prevented the locking piston from movingimmediately to its arresting position, when e.g. the engine hydraulicsys-tem had been switched off. The locking effect only occurred when thepressure had been reduced to a certain extent by leakage at the lockingarea of the locking piston. Such a de-lay is prevented by the structuraldesign chosen.

[0009] In accordance with an advantageous embodiment, the locking areacan be provided in the form of a locking opening in a locking plungerwhich extends away from the operating sec-tion, at least a portion ofthe locking means of the tensioning piston extending through saidlocking opening. The locking opening guarantees that a pressure mediumin its interior will produce force components over the whole area ofsaid opening and that the forces will compensate each other in such away that the actuation of the locking piston will not be supported. Thisis a simple structural measure by means of which the locking area can bedesigned such that is not subjected to the influence of pressure forces.

[0010] In addition, the locking opening may be provided with a lockingprojection, which is ar-ranged on the inner surface of said lockingopening on one side thereof and which is used for engagement with thelocking means of the tensioning piston. Such a locking projection on theinner side does not have any influence on the force conditions in theoperating direc-tion of the locking piston and guarantees nevertheless areliable engagement with the lock-ing means of the tensioning piston.

[0011] According to one variant, the locking means of the tensioningpiston may comprise a lock-ing rod provided with teeth and extendingthrough the locking opening of the locking piston. The operating pathsof the tensioning piston and of the locking piston will therefore crossand individual components of the two pistons will interengage. A verycompact and very robust structural design is provided in this way.

[0012] The locking rod can have a circular basic cross-section, thelocking opening in the locking plunger being then implemented as anelongated hole which is adapted to this basic cross-section. This length(seen in the direction of the longitudinal axis of the locking piston)of the elongated hole can then correspond to at least to the operatingstroke of the locking piston between the release position and thearresting position. This means that the locking rod and the lockingpiston part providing the locking opening can also mutually guidethemselves, since the amount of play must be chosen precisely such thatthe locking rod can be dis-placed freely in the elongated hole in therelease position. In the case of such a variant, the locking rod canalso be implemented as an extension of the actual tensioning pistonhaving a smaller diameter. However, also other cross-sections arepossible instead of the circular cross-section.

[0013] When, in accordance with one variant, the inner surface of thelocking opening is provided on one side thereof with an undercut portionwhich merges with the locking projection, the locking opening providesalso in the arresting position a contact shoulder for close contact withthe locking rod. When the locking piston is implemented as a plasticcomponent or as a cast member, this undercut portion will also reducethe accumulation of material.

[0014] In accordance with one embodiment, the tensioning piston isguided in a housing, a pres-sure chamber is formed between said housingand said tensioning piston, the locking means extend from the inner tothe outer side of said pressure chamber, and the teeth are locatedoutside of said pressure chamber in the fully retracted position of thetensioning piston. This is to be regarded as an additional measure fordisplacing the locking area of the locking piston away from the pressurearea of a fluid-operated tensioning piston. Depending on the structuraldesign of the housing, the locking area will then only be subjected to aleakage flow of the fluid. Oscillating conditions occurring in thepressure medium during operation of the tensioning means will thereforenot affect the locking piston.

[0015] According to a preferred embodiment, the locking piston can beguided in a housing such that it is separated from a pressure chamber ofthe tensioning piston. The two pistons can also be arranged in a commonhousing; in this case, only the locking means and the locking area crosseach other and are adapted to be brought into engagement with oneanother.

[0016] According to a further embodiment of the tensioner for aninternal combustion engine hav-ing an engine oil circuit, the pistonarea of the locking piston can be acted upon by the hy-draulic pressureof the erigine oil circuit. By selecting an advantageous supply means,it can here be guaranteed that hydraulic oscillations of the typeoccurring in the area of the pres-sure chamber of the tensioning pistonare decoupled as far as possible from the operation of the lockingpiston. In the simplest case, this delimitation is effected via anon-return valve.

[0017] In the following, an embodiment of the present invention will beexplained in detail making reference to a drawing, in which:

[0018]FIG. 1 shows a hydraulic chain tensioner according to the presentinvention in a fully sec-tional view,

[0019]FIG. 2 shows the chain tensioner of FIG. 1 in a sectional viewalong line II-II and

[0020]FIG. 3 shows the chain tensioner of FIG. 1 in a sectional viewalong line II-II.

[0021] The chain tensioner 1 shown in FIG. 1 to 3 is provided with alocking function, in particular when the hydraulic circuit is switchedoff.

[0022] The chain tensioner 1 essentially comprises a cast housing 2which consists e.g. of an alu-minium die casting, a tensioning piston 3which is axially guided in said housing, and a lock-ing piston 4 whichis guided in said housing 2 at right angles to said tensioning piston 3.The tensioning piston 3 is guided in a cylindrical bore 5 in saidhousing 2 and comprises a cylindrical guide sleeve 6 and a piston head 7press-fitted into said guide sleeve and con-sisting e.g. of a suitableplastic material. The guide sleeve 6 is preferably produced from steel.A portion of the piston head 7 rests on the end face of the guide sleeve6 so that it is guaranteed that an endless driving element, e.g. achain, or the tensioning area of a ten-sioning rail will come intocontact only with the piston head 7. In the interior of the guide sleeve6, the piston head 7 merges with a cylindrical locking rod 8 having, atthe free end thereof, locking teeth 9 acting as locking means. Thelocking teeth are implemented as a circumferentially extending annulargroove having a triangular cross-section, so that a sawtooth profile isformed in cross-section. The direction of the sawtooth profile is chosensuch that an extension, but not a retraction, of the tensioning piston 3can be blocked. Be-tween the piston head 7 and the locking rod 8 ahollow-cylindrical annular space 10 is pro-vided in the middle area ofsaid locking rod 8, said annular space having arranged therein a helicalcompression spring (not shown). The compression spring rests on the back11 of the piston head 7 and on the base 12 of the bore 5.

[0023] The chain tensioner 1 is shown at a position of transport. Atthis position, the tensioning piston 3 is fully retracted and arrestedby a securing pin 12. The compression spring, not shown, in the annularspace 10 is compressed in its maximum tensioning condition. When thechain tensioner 1 has been installed with the aid of the fasteningsleeves 13 and 14 on the housing 2, the securing pin 12 is removed,whereby the transport position will be re-leased. The tensioning piston3 is then in tensioning contact with e.g. the contact area of atensioning rail, which, in turn, is pressed against a chain.

[0024] From the sectional view of FIG. 3 it can be seen that the annularspace 10 and the free space of the bore 5 extending below the tensioningpiston 3 can communicate via a hydrau-lic channel 37 in the housing 2with the engine oil hydraulic system of an internal combustion engine towhich the chain tensioner 1 is secured. This means that engine oil canflow into this pressure chamber via a non-return valve 36. The hydraulicfluid flows into the hy-draulic channel 37 via the non-return valve 36which is press-fitted into a lateral bore 38 of the housing. Thishydraulic channel extends parallel to the locking teeth 9 and parallelto the bore 29 in the bottom. Also a locking plunger 16 extends in thishydraulic channel 37 so that both the locking plunger 16 and the lockingteeth 9 on the locking rod 8 are subjected to the hydraulic pressure.Due to the displaced section along line II-II, the non-return valve 36is shown in FIG. 2 in a view which is only a fragmentary sectional view.In the operating state, the tensioning function is primarily applied bythis hydraulic pressure whose force exceeds the tensioning force of thespring. The hydraulic fluid in the pressure chamber is thereforesubjected to the vibrations of the tensioning piston 3 and relief onlytakes place via leakage flows. When the engine oil hydraulic pressureincreases, the tensioning force of the tensioning piston 3 will increaseas well.

[0025] The locking piston 4, which is displaceable in the housing 2 atright angles to the tensioning piston 3, comprises a cylindricaloperating section 15 and a locking plunger 16 arranged on said operatingsection 15. Only the locking plunger 16 crosses the locking rod 8 of thetensioning piston 3. The operating section 15 is provided with anannular piston area 17. In addition, said operating section 15 is guidedin a cylindrical bore 18 such that it is axially displaceable therein.Between the piston area 17 and the base area 19 of the operating sectiona pressure chamber 20 is defined, which communicates via a supplypassage 21 with the engine oil hydraulic system. It follows that, whenpressure is built up in the pressure chamber 20, this will have theeffect that the locking piston 4 is displaced upwards (cf. FIG. 1) to arelease position. In the unloaded condition, the locking piston 4 ispressed down-wards into an arresting position (cf. FIG. 1) via acompression spring 22 which is arranged in a cylindrical bore 23 of theoperating section 15 and which rests on a support disk 24 se-cured by aretainer ring 25, said cylindrical bore 23 being open at the rear. Thespring force is dimensioned such that, in the operating state, it willbe bridged by the pressure in the pressure chamber 20.

[0026] The locking plunger 16 is rectangular in cross-section andextends in a guide opening 26 through the housing 2 and projects beyondsaid housing on one side thereof. In addition, the locking plunger 16 isprovided with hollow spaces 27, which permit said locking plunger 16 tobe also implemented as an injection-moulded part consisting of plasticmaterial (so as to avoid accumulations of material).

[0027] The bore 5 for the tensioning piston 3 and the guide bore 26 forthe locking plunger 16 communicate only via a small connection opening28, which is just large enough to permit passage of the portion of thelocking rod 8 provided with the locking teeth 9, and the hy-draulicchannel 37. The free end of the locking teeth 9 is received in anddisplaceably guided in the bore 29 in the bottom of the housing.

[0028] The locking teeth 9 of the locking rod 8 extend through a lockingopening 30 provided in the locking plunger 16. This locking opening 30extends at right angles to the operating direc-tion of the lockingpiston 4. The inner circumference of the locking opening is fullydefined by the locking plunger 16 so that said locking opening can onlybe engaged from the left or from the right (cf. FIG. 1). In addition,when seen in a cross-sectional view, the locking open-ing 30 isimplemented as an elongated hole, which is adapted to thecross-sectional shape of the locking teeth 9 of the locking rod 8. Thelength of said elongate hole is chosen such that it exceeds the lengthof the operating path of the locking piston 4. The locking opening isprovided on one side thereof with an undercut portion 31 whosecross-section is, how-ever, designed such that, at the arrestingposition, the locking teeth 9 of the locking rod 8 will come intocontact with a shoulder 32 of the locking opening so that the undercutportion 31 will remain free. On one side of the locking opening 30, alocking projection 33 projects partly into said undercut portion 31 andpartly into said locking opening 30. The end face of said lockingprojection 33 has an arcuate form so that it will precisely fit inbetween the lock-ing teeth 9. The locking projection 33 is designed suchthat it is adapted to be brought into engagement with a respectiveannular groove between the teeth of the locking teeth 9. Also saidannular groove is triangular in cross-section, the part of said groovemerging with the undercut portion 31 being, however, rounded.

[0029] At the side of the bore 18, a vent channel 34 is arranged throughwhich also a leakage flow can escape from the pressure chamber 20.

[0030] In the following, the mode of operation and the function of thechain tensioner 1 will be ex-plained in detail.

[0031] The chain tensioner 1, which is shown in the transport state, issecured via the sleeves 13, 14 to an engine block of an internalcombustion engine. Subsequently, the cotter pin 12′ and the securing pin12 are removed so that the tensioning piston 3, which is acted upon bythe compression spring, will be extended. The interaction of thecompression spring 22 and of the locking piston 4 and of the compressionspring (not shown) of the tensioning piston 3 is chosen such that thelocking teeth slip through on the locking projection 33. An equilib-riumwill be established between the tensioning piston 3 and the medium to betensioned, especially a tensioning rail. Via the suitably designedconnection surface 35 (laterally on the housing 2), a connection to thehydraulic circuit of the internal combustion engine is automaticallyestablished due to fastening via the sleeves 13 and 14. The supplychannel 21 for the locking piston 4 as well as the supply channel 37 forthe tensioning piston 3 will then communicate with the engine oilhydraulic system. Alternatively to the transport securing meanscomprising the cotter pin 12′ and the securing pin 12, the interactionof the compression spring 22 and of the locking piston 4 and of thecompression spring (not shown) of the tensioning piston 3 can also bechosen such that the locking teeth engaging the locking projection 33serve as transport securing means. As long as the locking piston 4 isnot un-locked by the engine oil hydraulic pressure, the chain tensioner1 will therefore occupy a locked position.

[0032] Assuming now that the internal combustion engine is switched off,the tensioning piston 3 and the locking piston 4 will not have appliedthereto any hydraulic pressure. In this condition, the tensioning piston3 is prevented from retracting by the locking piston 4, which is forcedinto the arresting position by the compression spring 22. This meansthat, when the engine is being started, a retraction of the tensioningpiston 3 will be prevented in spite of strong forces occurring at thepiston head 7, before a suitable hydraulic pressure can build up in thehydraulic circuit. It follows that, in spite of the insufficienthydraulic pressure, a predetermined tension will always be given whenthe engine is started. As soon as a sufficient hydraulic pressure hasbuilt up after the start of the engine, the locking piston 4 will bedisplaced to the release position due to the pressure that builds up inthe pressure chamber 20. Also the hydraulic pressure in the pressurechamber of the tensioning piston 3 is in-creased such that thetensioning force will be applied mainly through this hydraulicpres-sure. This hydraulic pressure is load-dependent and increases inthe case of higher speeds, whereby the tension will be increased. Inthis condition, the tensioning piston 3 can operate in the normal way,as in the case of conventional hydraulic chain tensioners. The lockingteeth 9 can move freely within the locking opening 30 because thelocking projection 33 is retracted. Also hydraulic fluid penetrates intothe locking opening 30 through the connection channel 37 and theconnection opening 28. Due to the fact that said locking opening 30 isimplemented as a circumferentially closed elongated hole, the hydraulicpressure will, how-ever, not influence the operation of the lockingpiston 4. On the contrary, force components will be generated bothtowards the release position and towards the arresting position so thatthe hydraulic pressure will not influence the operating behaviour of thelocking piston 4 within the locking opening 30. Nor do the undercutportion 31 and the locking projection 33 produce any effect in theoperating direction, since what matters is the area projectedper-pendicularly to the operating direction. It follows that theoperation of the locking piston 4 is only influenced by the compressionspring 22 and the hydraulic pressure in the pressure chamber 20. Thepressure chamber 20 is, however, decoupled from the pressure chamber ofthe tensioning piston 3 and its pressure fluctuations caused byvibrations on the endless driving element, e.g. the chain. A reliableextension and retraction behaviour of the locking piston 4 is achievedin this way.

[0033] According to a further embodiment, the locking piston could alsobe operated electrically or pneumatically.

1. A tensioner for endless driving elements, such as chains, belts etc.,comprising a ten-sioning piston (3) provided with locking means (8, 9),and a locking piston (4) which is implemented such that it is adapted tobe engaged with and disengaged from said lock-ing means (8, 9) so as toarrest or release the movement of said tensioning piston (3),characterized in that the locking piston (4) comprises an operatingsection (15) caus-ing said locking piston (4) to move to the arrestingposition and to the release position, and a locking area (30, 33) usedfor engagement with said locking means (8, 9) of the tensioning piston(3) and arranged separately from said operating section (15).
 2. Atensioner (1) according to claim 1, characterized in that the operatingsection (15) of the locking piston (4) is provided with a piston area(17) which is adapted to have ap-plied thereto an operating pressure ofa hydraulic fluid, the operating direction of said piston area (17)being directed towards the release position of the locking piston (4).3. A tensioner (1) according to claim 1 or 2, characterized in that aspring means (22) is provided, which acts on the operating section (15)of the locking piston (4), said spring means (22) being effective in thedirection of the arresting position of the locking piston (4).
 4. Atensioner (1) according to one of the claims 1 to 3, characterized inthat the locking area (30, 33) of the locking piston (4) is designedsuch that a hydraulic force balance is caused.
 5. A tensioner (1)according to one of the claims 1 to 4, characterized in that the lockingarea is provided in the form of a locking opening (30) in a lockingplunger (16) which ex-tends away from said operating section (15), atleast a portion of the locking means (8, 9) of the tensioning piston (3)extending through said locking opening (30).
 6. A tensioner (1)according to claim 5, characterized in that the locking opening (30) isprovided with a locking projection (33), which is arranged on the innersurface of said locking opening (30) on one side thereof and which isused for engagement with the locking means (8, 9) of the tensioningpiston (3).
 7. A tensioner (1) according to claim 5 or 6, characterizedin that the locking means (8, 9) of the tensioning piston (3) comprisesa locking rod (8) provided with teeth (9) and extending through thelocking opening (30) of the locking piston (4).
 8. A tensioner (1)according to claim 7, characterized in that the locking rod (8) has acircular basic cross-section, and that the locking opening (30) isimplemented as an elongated hole which is adapted to this basiccross-section, the length of said elongated hole corresponding at leastto the operating stroke of the locking piston (4) between the releaseposition and the arresting position.
 9. A tensioner (1) according toclaim 8, characterized in that the inner surface of the lock-ing opening(30) is provided on one side thereof with an undercut portion (31) whichmerges with the locking projection (33).
 10. A tensioner (1) accordingto one of the claims 7 to 9, characterized in that the tensioning piston(3) is guided in a housing (2), that a pressure chamber is formedbetween said housing (2) and said tensioning piston (3), that thelocking means (8, 9) extend from the inner to the outer side of saidpressure chamber, and that the teeth (9) are lo-cated outside of saidpressure chamber, at least in the fully retracted position of thetensioning piston (3).
 11. A tensioner (1) according to one of theclaims 1 to 10, characterized in that the locking piston (4) is guidedin a housing (2) such that it is separated from a pressure chamber ofthe tensioning piston (3).
 12. A tensioner (1) for an internalcombustion engine having an engine oil circuit according to one of theclaims 1 to 11, characterized in that the piston area (17) of thelocking piston (4) is acted upon by the hydraulic pressure of the engineoil circuit.